The field of the invention is shaped-beam electron beam systems employing simultaneous multiple beams.
As circuit dimensions continue to shrink while device complexity grows, the number of pixels required to expose a chip pattern for reticle fabrication grows at an enormous rate. A mask writer with a high throughput has a strong competitive advantage over systems with lesser throughput. There are a number of ways in which mask writers have tried to gain an edge in throughput. For single pixel round beam systems, such as the Mebes 5500 manufactured by ETEC systems, the solution has been to increase the brightness of the pixel in order to decrease the time required to expose the pixel. This, coupled with a fast blanking system and a large pixel that compromises resolution for speed has permitted this technology to remain competitive through the 130 nm node, possibly to the 100 nm node. Those skilled in the art doubt that this technology is extendable to the 70 nm node and below. Another approach to enhancing the throughput of a mask writer has been to expose pixels in parallel. This has been accomplished in the IBM EL- series of mask writers through the use of a variable shaped spot. In this way, hundreds to thousands of pixels may be exposed in parallel. Since the brightness is usually less than that of a single pixel system, the net gain in throughput of a variable shaped beam system over a single pixel system is usually on the order of 5-10X. Other systems have taken the parallel pixel scheme even further, such as a character projection system found in systems by Hitachi or the projection e-beam steppers, such as the IBM/Nikon Prevail program. Neither of these are suitable for maskmaking, the character projection system does not have the flexibility to deal with the spectrum of features to be found on all masks, while Prevail is a wafer writer and requires the use of a reticle for the exposure.
For a shaped beam system to be efficient, the full spot should not be too much larger than the typical feature found in the pattern. If it is, beam current that could be used to expose the pattern is being wasted as it is masked off on the shaping aperture. It is estimated that by the time the 50 nm node is reached, a shaped beam system would be required to flash over 1 trillion spots to form a mask. In order to complete a mask in under 4 hours, no more than 10 ns can be spent exposing the average spot. Timing granularity for precise dose control would be required to operate in the 25-50 ps range. For a single spot shaped beam system, this represents a formidable challenge. One way to address this situation is to use multiple shaped beams in parallel. Four beams at 40 ns, can provide the same throughput as a single beam at 10 ns, while 16 beams can operate at the rather pedestrian rate of 160 ns and still accomplish what one beam can do in 10 ns.
Multiple round beams have been known as a throughput advantage for some time. They are commonly used in laser writers, such as the Alta series of tools manufactured by ETEC. Arrays of microcolumns, such as demonstrated by Chang et. al. are a form of round electron multibeam concepts. Groves and Kendall (U.S. Ser. No. 05/981962 and U.S. Ser. No. 05/962859) have described a multibeam shaped beam lithography system that makes use of uniform electric and magnetic fields to form images from a microlithographic shaping system. The distributed system described by Groves and Kendall also employs a separate contrast aperture for each beamlet, eliminating problems with Coulomb interactions. The lithography system they describe is fundamentally different from the step and repeat architecture used in the IBM EL-series of mask writers and could not be retrofitted onto a single spot system. The 1:1 imaging between the apertures and the target in the Groves and Kendall system places very stringent requirements on the aperture for good image fidelity.
The invention relates to a multiple shaped beam system that is compatible with existing single spot shaped beam system, allowing a single shaped spot system to be upgraded to a multibeam system.
A feature of the invention is the use of a datapath for driving the multibeam column, that makes full use of an existing shaped beam data path, together with the extensions that enable a multibeam environment.
Another feature of the invention is the addition of a new section of the system that displaces the set of n shaped beamlets to desired relative position after which the set of beamlets is directed as a whole onto the wafer or other workpiece.